1. Field of Invention
The present invention relates generally to the field of servers and pertains more particularly to a system for providing reliable client/server sessions by controlling the consumption of resources between or among arriving messages to a server.
2. Discussion of the Prior Art
Servers are commonly employed for sharing of information among large numbers of computer systems or similar devices. A computer system or similar device that communicates with a server is usually referred to as a client of the server and the server is often part of a host system. A client and a host typically exchange messages via a communication network using a predetermined protocol. Such protocols are usually arranged in a client/host model in which a requesting client transfers a request message to a host and the host in turn takes an appropriate action depending on the content of the request. Typically, the appropriate action for the request includes the transfer of a response message to the requesting client.
Prior protocols typically do not allow for the establishment of a persistent session between the client and the host in the traditional sense in which a local terminal establishes a session on a computer system. Instead, any session-like information is usually implied in the content of the messages exchanged between the client and the host. Such a communication protocol may be referred to as a xe2x80x9cstatelessxe2x80x9d protocol. Such stateless protocols include protocols associated with Internet communication including the Internet Protocol (IP), the User Datagram Protocol (UDP), the Simple Mail Transfer Protocol (SMTP), and the Hypertext Transfer Protocol (HTTP), as well as the Network File System (NFS) Protocol.
A client that accesses a host commonly engages in an extended transaction with the host. Such an extended transaction typically involves the exchange of multiple messages between the client and the host. For example, an NFS client typically issues multiple request messages to an NFS server while retrieving a file from the NFS server. Similarly, an HTTP client typically issues multiple request messages to an HTTP server while browsing through web pages contained on the HTTP server. Such transactions that involve the exchange of multiple messages between a client and a server are hereinafter referred to as sessions.
Servers commonly have a large pool of potential clients which may issue request messages. For example, an HTTP server connected to the world-wide-web has potentially millions of clients from which it may receive requests. Prior servers that are adapted for stateless protocols typically respond to each request in the order in which it is received, that is, on a first-come-first-served basis regardless of the source of the request.
In the present context, the term xe2x80x9cquality of servicexe2x80x9d refers to the ability of a host both to provide quick response to a request message and to complete an entire session. As a particular host becomes more popular, and due to that popularity receives more requests, the processing resources of the host can become stretched. For example, due to heavy traffic, a host may not be able to respond to a request at all, or the host may not provide a timely response which can cause a client to xe2x80x9ctime-outxe2x80x9d and generate an error. Poor quality of service can have significant results, as users may become frustrated and simply give up trying to reach a particular host, or more significantly, the sponsor of the host may lose sales or fail to communicate needed information to any or all clients.
Two techniques are generally used to alleviate quality of service problems. First, more processing capacity can be added to the host, typically by either replacing the host with another, more powerful computer, or by providing multiple computers in parallel and delegating new request messages to different ones of the multiple computers. While this first technique presents an effective way of reducing some quality of service problems, it is not always practical. For example, sometimes, due to inadequate planning, budgetary constraints or space constraints, additional processing capacity simply cannot be added. Other times, if demand for a host is not properly forecast, there may be a long lead time before additional processing capacity can be purchased and implemented.
A second technique calls for applying xe2x80x9cadmission control,xe2x80x9d where only a certain set number of client request messages are processed (xe2x80x9cadmittedxe2x80x9d) and the remainder are refused. Of the requests which are in fact admitted, all are ideally handled in an expedient manner without degradation of quality of service as to those admitted requests. An advantage of this technique is that admission control can be implemented in software, thus facilitating quick, inexpensive use with little advance notice. Unfortunately, typical admission control mechanisms operate by admitting messages on a message-by-message basis, and so, these typical admission control techniques do not provide an adequate solution for multiple-message sessions. Also, the requests which are not admitted to the host are generally not handled at all, such that a client is not informed that the request has been refused or the client, if informed, is simply asked to xe2x80x9ctry again later.xe2x80x9d Typically, a refused client must try repeatedly to obtain service with no guarantee that future requests will be processed. For these reasons and others, techniques generally used to alleviate quality of service problems are not always successful.
A definite need exists for a resource control system having an ability to alleviate quality of service problems. In particular, a need exists for a resource control system which responds to all request messages based on their relationship to new or existing sessions. Ideally, such a system would operate by fairly sharing resources amongst the sessions when there is a contention for those resources. With a system of this type, resource control would provide a reliable means of finishing more sessions with high quality of service. A primary purpose of present invention is to solve these needs and provide farther, related advantages.
A session based resource control system for a server is disclosed including a resource controller that receives a stream of arriving messages from one or more clients targeted for the server. The resource controller relays to the server the messages and a corresponding resource share for each message as a stream of resource allocated messages. The resource share is based on the resource rate for that session as determined by a resource monitor. The server then processes each message in accordance with its resource share and generates a stream of completed messages. The objective is for the resource control system to achieve fairness whenever there is contention for resources between or amongst the sessions.